Optical activation of cultured neurons using ultra-short pulse laser

Abstract

The paradigm of experimental models in modern neuroscience and neural engineering has been rapidly evolving from 2D to 3D environments. A variety of techniques have emerged as important tools for controlling action potential firing of a single neuron in 3D environments. Here, we report that a focused femtosecond light activates an unmodified neuron in a 3D environment, producing repetitive action potentials without insertion of any external materials. To further characterize this method, a new microfluidic system was developed to optically stimulate a neuron and electrically record its signals for a long duration. This was combined with the microfluidic technique and electrode measurement under the microscope. This approach allowed precise and rapid stimulation of a single neuron at multiple points, and systematic analyses of neural and axonal responses using a spike sorting technique. We assessed the property, efficiency, and safety of this optical stimulation using the focused femtosecond light. We also demonstrated that the femtosecond light stimulated a neuron successfully in 3D environments. Furthermore, the studies on the underlying mechanism indicated that the neural response to femtosecond light was caused by intracellular calcium elevation from the internal calcium store through supra-threshold excitation of the soma. Although several factors remain to be determined regarding femtosecond light irradiation, we expect that this technique will avoid many of the problems inherent to electrodes, such as invasiveness and lack of specificity, and thus, could aid in scientific discoveries and in engineering experimental approaches. Furthermore, the femtosecond light coupled with an appropriate optical probe can be employed for in vivo neural stimulation. This may lead to new therapeutic approaches with rapid optical regulation of excitation and inhibition without genetic modification and external interruption of the cellular function.